When you are respawning, and are in the class select screen, then if you press the comma ( , ) aka the class select key, without choosing a class, then you can stay in class select infinitely, because the respawn timer refreshes automatically.

• Now whenever you die or killbind, then first spectate the person you want to spectate.
  
• Now go into class select screen, don't choose any class, just stay there.
  
• Now you can specate them forever as long as you stay in the class select screen.

If you want to change target, go out of spectate and simply change targets, but quickly go back to class select screen.

The respawn timer at some point will only refresh till 5 seconds, so you have to be quick when changing target, you can also go back to class select screen to refill the timer if it's almost over.

Example of how this looks like with Flawhud:

Do experiment with other huds too, just look out for how their class select screen looks. Here's some quick recommendations based of on their class select screens:

• panzerhud[tf2huds.dev]
  
• ahud[tf2huds.dev]
  
• 7HUD[tf2huds.dev]
  
• budhud[tf2huds.dev]
  and many many more, go explore :3

Happy spectating soldier!